It is a Pilot Decision to report a Hard/ or Overweight LDG. No entry no work
Yeah, when a 747 has one and the crew does not to admit it, you end up with crunched flaps as they often shift on a hard landing and crew are supposed to leave them extended, I can only speak of Classics.
The hard landing indicator on the dc-10/md-11 is the positive pressure relief valves, a hard landing knocks them open over the flapper every time.
But unfortunately you are correct for most cases, unless you end up with a random DFDR dump that would reveal the hard landing, a DFDR read is the only definitive way to determing the ft/second impact.